The present invention relates to a communication terminal with an electromagnetic transmission or receiving antenna and at least one energizable device for acoustic sound conversion.
Communication terminals are subject to a constant size-reduction process. As such, it is essential to make optimum use of the available space in the communication terminal. The function of individual components is optimized and their size minimized. However, this can only be achieved subject to compromises with respect to the function and size of the components. This also affects components, the performance of which depends directly on their geometric dimensions. Examples of such are loudspeakers and their effective membrane surface or a planar antenna as-used in a mobile telephone and its dimensions.
A communication terminal is disclosed in WO 00/38475, the housing of which houses a loudspeaker and an antenna. The loudspeaker is configured as an acoustic resonance chamber and it is located either wholly or partially in the electromagnetic resonance chamber of the antenna serving as the support.
A radio telephone is disclosed in WO 00/30268 which includes a patch antenna. This patch antenna has a “speaker 35” mounted on one side of the antenna, connected to a “front face” through holes in the antenna.
Minimization of the individual components is achieved by combining different functions in one component. In the case of a mobile telephone, for example, an electrodynamic acoustic converter, also referred to as a receiver, is used. The receiver includes a number of acoustic sound conversion functions.
The main function of the receiver is its operation as an earpiece for the typical use of a mobile telephone at the ear.
The receiver is also used for ringtone generation, sometimes referred to as buzzer function. The receiver here is operated as a buzzer.
Mobile radio terminals also often includes a handsfree speaking or listening option with an additional loudspeaker function for open listening. In this case, the receiver is operated as a loudspeaker.
All three functions impose very different requirements on the receiver.
In the case of ringtone generation, high acoustic pressure levels are generated via the receiver. These are typically around 100 dB(A) at a distance of 5 cm from the receiver. With typical membrane diameters of 13 mm, high acoustic pressure levels are generated via resonant frequency response on the part of the receiver in the frequency range of 2000 Hz to 4000 Hz.
If the receiver is operated as an earpiece for a standard earphone, it operates on a more or less closed air volume in the ear, known as the acoustic load. It should then have a flat frequency response in the range of 300 Hz to 3600 Hz.
The handsfree listening option also requires the generation of high acoustic pressures. Radiation with a flat frequency response is necessary in order to reproduce speech naturally. However, small membrane diameters only allow higher acoustic pressures, typically upwards of 700 Hz, resulting in compromises in sound quality. The receiver here operates on an open air volume.
When the functions of operation as an earpiece for an earphone and buzzer function for ringtone generation are combined, their frequency response requirements are conflicting. In the case of ringtone generation, a considerable amount of electrical power is converted, resulting in significant heating of the receiver. This heating reduces the life of the receiver and modifies its frequency response in the long term.
When the additional function for handsfree listening and the function of operation as an earpiece in a receiver are combined, the associated acoustic loads of open or closed air volume, on which the receiver operates, are different.
If all three functions described are combined in one receiver, compromises are made with all three functions. Possible limitation of these compromises by digital signal processing is only possible to a limited degree, without significantly restricting the required dynamic range or generating other unwanted secondary effects, such as noise or distortion.
In existing mobile telephones these three functions are combined in a very small receiver.
An object of the present invention, therefore, is to create an acoustic sound conversion function that takes up little space and does not restrict other acoustic sound conversion functions in a communication terminal.